Improve code documentation: increment → decrement for decrement metho…

…ds (#14200)

Some methods use the verb 'increment' both for increment and decrement
methods. This change fixes this issue and standardizes the comments
of the decrement methods.

src/Illuminate/Cache/ArrayStore.php

@@ -56,7 +56,7 @@ public function increment($key, $value = 1)
     }
 
     /**
-     * Increment the value of an item in the cache.
+     * Decrement the value of an item in the cache.
      *
      * @param  string  $key
      * @param  mixed   $value

src/Illuminate/Cache/DatabaseStore.php

@@ -128,7 +128,7 @@ public function increment($key, $value = 1)
     }
 
     /**
-     * Increment the value of an item in the cache.
+     * Decrement the value of an item in the cache.
      *
      * @param  string  $key
      * @param  mixed   $value

src/Illuminate/Cache/NullStore.php

@@ -52,7 +52,7 @@ public function increment($key, $value = 1)
     }
 
     /**
-     * Increment the value of an item in the cache.
+     * Decrement the value of an item in the cache.
      *
      * @param  string  $key
      * @param  mixed   $value